1. Field of the Invention
The present invention relates to an optical switching unit including a plurality of optical switches.
2. Description of Relevant Art
In recent years, as a new type of signal transfer system, there has been proposed an optical transfer system, in which an optical fiber for the transfer of a beam of light consisting of a plurality of component rays of different wavelengths is employed as a transfer cable. Particularly, as an example of implementation of such optical transfer system, there is known an optical detection system with an optical switch element disposed in the route of the transfer cable.
As an example of such optical switch element, in Japanese Patent Laid Open No. SHO 56-8103 (1981), there is proposed an optical switch of such constitution as shown in FIGS. 5a and 5b of the accompanying drawings.
As shown in FIG. 5a, the optical switch designated at reference character A includes a branching device 102 positioned in the route of a main optical fiber 101 for transfer service, the device 102 consisting of a spectroscopic element for extracting or reflecting a component ray of particular wavelength and transmitting other component rays of light, a pair of optical fibers 104, 105 constituting a light-conductive bypass for transferring the reflected ray of light, a light-shielding plate 106 interposed between the respective confronting end faces of the optical fibers 104, 105, and a joining device 103 consisting of a spectroscopic element for reflecting only the component ray of particular wavelength transferred through the optical fibers 104, 105 and transmitting other component rays of light.
The branching device 102 is composed of an interference filter, a diffraction grating, or a prism, while the joining device 103 is composed of a half mirror or an interference filter. Moreover, the light-shielding plate 106 consists of a plunger actuatable such as by a solenoid.
The component ray of particular wavelength transferred through the optical fiber 101 is thus interruptable by the shielding plate 106. The optical switch A is permitted to detect the state of movement of the plate 106 by detecting the existence of the ray of particular wavelength at the outlet side of the optical fiber 101.
The optical switch A is applicable to a detection system such as shown FIG. 5b. Namely, the optical fiber 101 employed in the form of an optical cable is provided at the light source end thereof with three light sources Rs, Gs, Bs generating red, green, and blue colors, respectively, and a joining device 107 for composing a composite ray of light from the rays of light generated at the light sources Rs, Gs, Bs and feeding the composite ray to the optical cable 101. Moreover, in the route of the optical cable 101, there is provided three optical switches A1, A2, A3 connected in series and each respectively adapted to interrupt no more than one of the component rays as generated to be conducted from the light sources Rs, Gs, Bs. Also, the optical cable 101 has at the detection-element end thereof a joining device 108 for separating the transferred composite ray of light into the three components of red, green, and blue colors.
In the above-mentioned system, the optical switches A1, A2, A3 have their light-shielding plates each respectively adapted to selectively take "on" and "off" positions in response to the condition object to be detected. As a result, the optical switches A1, A2, A3 are permitted to sense a quantity of a state of the object, such as electronic current, voltage, temperature, and pressure. As a matter of course the optical switches A1, A2, A3 can be employed purely as on-off switches.
An example of such system is proposed in Japanese Patent Laid-Open No. SHO 56-149840 (1981), which discloses an optical detection system of such a constitution as shown in FIG. 6 of the accompany drawings.
In FIG. 6, designated at reference numeral 200 is the optical detection system, which is adapted for the detection of the on-off state of the switch of a plurality of terminal devices, while having substantially the same use as the detection system of FIG. 5b.
The optical detection system 200 includes a main device 201 having therein a light source 202 composed such as of a tungsten halogen lamp generating a continuous emission spectrum and a converging lens 203, an optical cable 204 adapted for light transfer between the main device 201 and the terminal devices 206, 207, 208, two pairs of reflectors 205 such as half mirrors for distributing component rays from the optical cable 204 to the terminal devices 206, 207, 208 and composing a composite ray of light by the component rays from the terminal devices 206, 207, 208, and a combination of branching filters 213 and an array of light-receiving elements 214 arranged in the main device 201 and adapted for the analysis of the composite ray conducted through the optical cable 204.
The terminal device 206 consists of a collimeter lens 211 for changing a component ray from the optical cable 204 into a flux of parallel rays, a converging lens 212 for leading the light flux from the collimeter lens 211 to the optical cable 204, a filter plate 210 interposed between the collimeter lens 211 and the converging lens 212, the filter plate 210 transmitting no more than a component ray of wavelength .lambda..sub.1, and a light-shielding plate 209 cooperating with the filter plate 210. At the terminal device 206, when the quantity of the state to be detected is in an "on" phase thereof, the filter plate 210 is positioned between lenses 211, 212 and, when it is in an "off" phase, the light-shielding plate 209 is positioned therebetween. Therefore, the terminal device 206 transmits, when such quantity is in the "on" phase, only the component ray of wavelength .lambda..sub.1 and, when it is in the "off" phase, no ray of light whatsoever. The constitution and function of other terminal devices 207, 208 are substantially the same as those of the terminal device 206, while respective component rays of light to be transmitted in their "on" phases are of wavelengths .lambda..sub.2, .lambda..sub.3, respectively.
In the above-mentioned detection system, for each terminal device, the quantity of the state to be "on" or "off" is detected by analyzing or detecting the component rays in the composite ray from the terminal device, with the branching filters 213 and the array of light-receiving elements.
In the foregoing two prior art optical switching and detection systems, an optical fiber or cable which is not an electrical conductor and free from electrical disturbances favorably permits the achievement of a detection system high in reliability with respect to noise, in comparison with a conventional detection system using an electric signal requiring shielding of an electric cable susceptible to noise.
Incidentally, with respect to the above two prior art systems, when comparing optical switches or certain members corresponding thereto, it will be understood that the optical switch according to the prior art example illustrated in FIG. 5b has a smaller number of component parts needed per the number of objects to be detected.
However, the optical switch of FIG. 5b has such problems as explained below.
The detection system illustrated in FIG. 5b has its optical switch portion schematized and its three light sources are assumed to be of three component rays of wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 (.lambda..sub.1 &lt;.lambda..sub.2 &lt;.lambda..sub.3), thereby obtaining a model shown in FIG. 7.
In FIG. 7, in addition to the optical switch A1, two optical switches A2 and A3 have respective spectroscopic elements 112, 113 and 122, 123, light-conductive bypasses 114, 115 and 124, 125, and light-shielding plates 116 and 126.
In the model of FIG. 7, the respective optical switches A1, A2, A3 are arranged in series along an optical transfer path of the optical cable 111, thus requiring, for separating the composite ray of light into respective component rays corresponding to the optical switches A1, A2, A3, the respective spectroscopic elements 102, 103; 112, 113; 122, 123 to have their filtration (reflection) characteristics selected so as to extract no more than respective component rays of corresponding wavelengths independently thereamong.
Accordingly, as shown in FIG. 8, the component rays of wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 are required to have their emission spectra (shadowed regions) covered by no more than respective reflection spectra B1, B2, B3 of corresponding electroscopic elements 102, 103; 112, 113; 122, 123, thus allowing no overlapping between respective pairs of neighboring reflection spectra B1, B2 and B2, B3. In other words, the case where, for example, the spectroscopic element 112 reflects the component ray of wavelength .lambda..sub.1 as well as that of wavelength .lambda..sub.2, the former ray is unable to avoid being subject to the interruption of both optical switches A1, A2, thus resulting in an erroneous detection of the on-off state of the light-shielding plate 106.
As a result, assuming the respective reflection spectra B1, B2, B3 of the optical switches A1, A2, A3 to be all of a predetermined wavelength band, the wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 of component rays must be selected to be spaced apart at intervals not smaller than the predetermined band width. Therefore, a predetermined total wavelength region of the optical transfer route 101 restricts to a considerable extent the degree of wavelength multiplication or the number of applicable optical switches. Further, the conventional limit switch is not normally assembled in a unit, thus being inconvenient.
The present invention has been achieved to effectively overcome the foregoing problems of conventional optical switches as applied to an optical detection system.